Polyamide resins are known to easily form hydrogen bond at amide group in the main molecular chain, to have strong intermolecular force owing to the hydrogen bond, and to readily show crystallinity. Because of the property to readily show crystallinity, the polyamide resins are superior to other resins in terms of heat resistance, resistance to hydrolysis, and other characteristics, and have dynamic strength.
Generally the polyamide resins are manufactured by ring-opening polymerization of ε-caprolactam, by polycondensation of a diamine with a dicarboxylic acid, and the like. Characteristics of thus manufactured polyamide resins can be varied by changing the kind of applied diamine, dicarboxylic acid, and the like.
Consequently, the polyamide resins can be used in various applications with the respective resin grades. For example, an aromatic polyamide in which an aromatic compound is used for one or both of diamine and dicarboxylic acid has a rigid aromatic ring in the main molecular chain, thus the aromatic polyamide has higher heat resistance than that of an aliphatic polyamide using an aliphatic compound, thereby being utilized in applications requesting high heat resistance.
Furthermore, the aromatic polyamides have low water absorbency, and are superior in the electric characteristics after absorbing water to the aliphatic polyamides. With the advantageous characteristics, the aromatic polyamides are widely used in electric-insulation applications and the like. The patent document 1 describes that an aromatic polyamide containing a phenoxy resin further decreases the water absorbency.
For the case that a resin is processed by extrusion using an extruder, adequate flowability is requested to the resin. For example, excess flowability induces problems of variations in extrusion rate, inclusion of bubbles, thickness deviation, and the like. Accordingly, the resin composition for that type of processing generally adopts the one having 30 or smaller MFR.
As described before, since the aromatic polyamide resins have rigid aromatic ring in the main molecular chain, they have fewer entanglements of molecules in molten state than those of aliphatic resins. Therefore, if an aromatic polyamide resin is used to improve the heat resistance and the water absorbency of resin composition, the flowability of the polyamide resin composition becomes excessive in the molten state, thus the polyamide resin composition may not be suitable for the above-described processing.
To this point, there is a proposal that the temperature of processing of the polyamide resin composition is decreased to near the melting point of the polyamide resin to decrease the flowability. The patent document 2 describes that a phenoxy resin is added to nylon 46 which is an aliphatic polyamide, thus to decrease the melting temperature, and then the injection molding is conducted at near the melting temperature.
The polyamide resins, however, show abrupt phase change near the melting point compared with other resins because they easily show crystallinity, as described above. Furthermore, the aromatic polyamide resins increase in flowability in the molten state compared with aliphatic polyamides such as nylon 46 owing to the above-described reason. Consequently, the aromatic polyamide resins significantly vary the flowability with a slight change in temperature near the melting point. Therefore, it is substantially difficult to decrease the flowability by decreasing the processing temperature to near the melting point because there is a need of precise control of resin temperature.
As a result, the conventional methods have a problem of difficulty in attaining a polyamide resin composition which has improved heat resistance and water absorbency while suppressing the deterioration in processability.
Patent Document 1
Japanese Patent Application Laid-Open No. Hei-3-237160
Patent document 2
Japanese Patent Application Laid-Open No. Sho-63-202655